selftests/landlock: Add audit tests for ptrace

selftests/landlock: Add audit tests for ptrace

Add tests for all ptrace actions checking "blockers=ptrace" records.

This also improves PTRACE_TRACEME and PTRACE_ATTACH tests by making sure
that the restrictions comes from Landlock, and with the expected
process.  These extended tests are like enhanced errno checks that make
sure Landlock enforcement is consistent.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-25-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>